This invention relates to a process for the selective production of lower aliphatic carboxylic acids and/or their corresponding esters by the carbonylation of the corresponding lower aliphatic alcohol and/or ester derivatives thereof, and, in particular to the selective production of acetic acid and/or methyl acetate by the carbonylation of methanol and/or methyl acetate.
The most widely used industrial process for production of acetic acid is the carbonylation of methanol, which is described generally in British patents 1,185,453 and 1,277,242 and U.S. Pat. No. 3,689,533, for instance. In that type of process, methanol is reacted with carbon monoxide or a carbon monoxide-containing gas in the presence of a rhodium- or iridium-containing catalyst, in the additional presence of a halogen (usually iodine)-containing promoter. Though widely used, nonetheless these processes require the use of expensive corrosion-resistant alloys due to the presence of iodide and result in production of low levels of iodine-containing byproducts that are difficult to remove from the acetic acid by conventional distillation. Some non-halide based catalyst systems have been investigated for this reaction, but none have been commercialized, primarily due to issues with catalyst lifetime and selectivity.
A number of patents describe processes in which methanol or a mixture of methanol and dimethyl ether is carbonylated in the presence of a catalyst. Typically the products are a mixture of acetic acid and methyl acetate, sometimes also including acetic anhydride. In those patents it is disclosed that one of the reactions that may occur is the carbonylation of dimethyl ether to form methyl acetate.
EP-A-0 596 632 discloses the preparation of an aliphatic carboxylic acid by contacting an aliphatic alcohol or a reactive derivative thereof with carbon monoxide in the presence of a copper, nickel, iridium, rhodium or cobalt loaded mordenite zeolite catalyst at high temperatures and pressures.
U.S. Pat. No. 6,387,842 discloses processes and catalysts for converting an alcohol, ether and/or ether alcohol feedstock to oxygenated products by reaction with carbon monoxide in the presence of a catalyst comprising a solid super acid, clay, zeolite or molecular sieve under conditions of temperature and pressure.
WO 2005/105720 discloses a process for the preparation of an aliphatic carboxylic acid, ester or anhydride thereof by contacting an aliphatic alcohol and/or a reactive derivative thereof with carbon monoxide in the presence of a copper, nickel, iridium, rhodium or cobalt loaded mordenite catalyst which has as framework elements, silicon, aluminium and also one or more of gallium, boron and iron.